1. Field of the Invention
The present invention relates to a method for quantitative bifurcation analysis of medical images, in particular angiographic images.
2. State of the Art
Angiography, in particular coronary angiography, refers to the process of investigating coronary arteries to determine the severity of any narrowing that may exist, such as by finding stenotic arteries. Quantitative Coronary Analysis (QCA) of single vessels has become a standard for guiding interventions and executing trail studies in coronary revascularization. However, angiographic analysis of lesions in or near a bifurcation presents a considerable problem since QCA for single vessels cannot handle more complex geometries. The definition of bifurcation herein is a splitting of a main tubular vessel into two or more further tubular vessels. For example, the left coronary artery bifurcates into the left anterior descending artery and the left circumflex artery.
QCA of a bifurcation involves automatic segmentation of the bifurcation. This can be followed by reconstructing a healthy state that includes the bifurcation area itself. The reference vessel diameter, which means the vessel's healthy diameter as computed by the QCA, is typically based on averages of the vessel “normal” parts before and after the bifurcation, respectively. So the greatest challenge for bifurcation lesion analysis is extracting the true reference vessel size of both the proximal vessel and its side branches. Conventional QCA detects vessel contours assuming minimal vessel tapering and cannot handle large steps in diameter caused by the bifurcation itself.
Most conventional QCA methods allow inputting a user-defined reference, which could eliminate the wrong reference definition. However this reference diameter would still only be valid on the one side of the bifurcation where the user defined the reference. This option is furthermore little reproducible such as through operator inaccuracy and subjectivity.
Currently no detailed publication has solved the above limitations. O. Goktekin et al, “A new quantitative analysis system for the evaluation of coronary bifurcation lesions: Comparison with current conventional methods”, Catheterization and Cardiovascular Interventions 69:172-180 (2007), evaluates a bifurcation package, in which the bifurcation is divided into three parts on each of which conventional QCA is applied. Goktekin describes a method for solving the reference problem by eliminating the central bifurcation area from the reference calculations. Therefore, the central bifurcation is still left out of consideration, both for calculating a diameter, and also for definition of a reference.